This section is from the book "Experimental Cookery From The Chemical And Physical Standpoint", by Belle Lowe. Also available from Amazon: Experimental cookery.
Meringues vary in the quantity of sugar added and in their use. Only soft and hard ones will be considered here.
Soft meringues. One general use for soft meringues is for pies. The factors determining to the greatest extent whether a desirable meringue is obtained are: the extent of beating the egg white, the adding of the sugar, the baking temperature and time, and an optimum proportion of sugar to egg white. Good meringues have been obtained by many methods, but the following method is successful for a majority of the experimenters. Beat the sugar into the egg white - preferably during the latter half of beating, but it may be added at the start - with a rotary egg beater, until the whites are stiff and shiny. The peaks are fairly stiff and the tip end only slightly rounded.
The sugar stabilizes the egg-white foam. Greater stabilization seems to be attained when the opportunity for solution is greater, i.e., in beating instead of folding. Since adding the sugar during beating increases the time required for obtaining a definite stiffness, there is less danger of over-beating. In some class problems less leakage of the meringue has occurred when the sugar was added in the above manner.
Since leaky meringues give undesirable moistness and slipperiness to the top of the pastry filling and make cutting difficult, how to prevent this leakage is a question frequently asked. The Institute of American Poultry Industries states that there seems to be no advantage in adding a small amount of water to the meringue. Although water increases the volume, there seems to be a tendency for the meringue to leak a short time after baking.
Insufficient beating of the egg white, especially if the sugar is folded instead of beaten into the meringue, after the sugar is added is sometimes a factor in causing leakage. Over-beating of the egg white before sugar is added may also increase the tendency to leakage.
Too small an amount of sugar to each egg white tends to give a less fluffy, less tender meringue and one lacking in sweetness. Too much sugar tends to give a gummy crust or one containing sugar crystals, though the amount of sugar that can be used to obtain a desirable meringue depends on the fineness of the sugar and perhaps on its rate of solution. In general, 2 tablespoons of fine or berry sugar per egg white give the best results. With ultra-fine crystals, as many as 3 tablespoons of sugar per egg white can be used; whereas with coarser granulated sugar, hitherto used more than at present, less than 2 tablespoons per egg is desirable. Powdered sugar containing starch is usually not satisfactory in meringues. Honey, sirup, or jelly may be used in meringues, but only 1 tablespoon per egg white. Red jellies often give a blue rather than a pink tinge to the meringue.
Baking necessarily requires a longer time at a lower temperature. All of the following temperatures have been used successfully, though a majority of the students working on meringues as special problems preferred 425° and 400°F.: 425°F. for 6 minutes, 400°F. for 8 minutes, 350°F. for 12 to 18 minutes, and 325°F. for 18 to 25 minutes. With temperatures below 325°F., the time is long, the meringue often shrinks after being removed from the oven, and dries too much.
Hard meringues. Hard meringues contain a larger proportion of sugar than soft meringues. Because of the high sugar content they have a fairly smooth, somewhat crystalline, crisp crust. They are usually puffy in appearance and are used for accompaniment to, as a foundation for, or as a dessert.
The optimum amount of sugar appears to be 4 to 5 tablespoons per egg white, the smaller quantity probably being preferable. Since acid increases the tenderness of egg white, its addition is desirable. About 1 to 2 cc. of vinegar per egg white may be used; but, since cream of tartar produces a more stable foam than acetic acid, the use of cream of tartar may be preferable. About 1 1/2 per cent of cream of tartar, or between 1/8 to 1/4 teaspoon of cream of tartar per egg white, is satisfactory.
The sugar is added in the same manner as for soft meringues, but, because of the larger quantity added, better results are usually obtained if it is added gradually.
Bake on heavy paper at as low a temperature as possible, 225° to 275°F., for 40 to 60 minutes, the time depending on the temperature and size of the meringues. If the meringue is eaten shortly after baking, the soft centers, if not entirely dried in baking, are not objectionable. However, they may be removed. If the meringues are to stand over night, the Institute of American Poultry Industries recommends letting them stand in the oven until cool, after the heat is turned off, in order to dry the centers.